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Data Center Networking with Multipath TCP Costin Raiciu University College London & Universitatea Politehnica Bucuresti Christopher Pluntke, UCL Adam Greenhalgh,

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Presentation on theme: "Data Center Networking with Multipath TCP Costin Raiciu University College London & Universitatea Politehnica Bucuresti Christopher Pluntke, UCL Adam Greenhalgh,"— Presentation transcript:

1 Data Center Networking with Multipath TCP Costin Raiciu University College London & Universitatea Politehnica Bucuresti Christopher Pluntke, UCL Adam Greenhalgh, UCL Sebastien Barre, Universite Catholique Louvain Damon Wischik. UCL Mark Handley, UCL UCL

2 Topology Data Center Networking Today Routing Resource Allocation FatTree, VL2, BCube, multi-rooted tree Random load balancing TCP Path Selection OSPF, VLANs, TRILL

3 Topology Data Center Networking Tomorrow Routing Resource Allocation FatTree, VL2, BCube, multi-rooted tree Random load balancing TCP Multipath TCP Path Selection OSPF, VLANs, TRILL

4 Data Centers are Important Cloud computing Economies of scale: networks of tens of thousands of hosts Cool apps Web search, GFS, BigTable, DryadLINQ, MapReduce Dense traffic patterns

5 Flexibility is Important in Data Centers Apps distributed across thousands of machines. Flexibility: want any machine to be able to play any role. But: Traditional data center topologies are tree based. Dont cope well with non-local traffic patterns. Many recent proposals for better topologies.

6 Traditional Data Center Topology … Racks of servers Top of Rack Switches Aggregation Switches Core Switch 1Gbps 10Gbps

7 Fat Tree Topology [Fares et al., 2008; Clos, 1953] Aggregation Switches K Pods with K Switches each K=4 Racks of servers 1Gbps

8 VL2 Topology [Greenberg et al, 2009, Clos topology] 10Gbps 20 hosts 10Gbps …

9 BCube Topology [Guo et al, 2009] BCube (4,1)

10 How Do We Use this Capacity? Need to distribute flows across paths. Basic solution: Random Load Balancing. Use Equal-Cost Multipath (ECMP) routing. Hash to a path at random. Use many differently rooted VLANs. End-host hashes to a VLAN; determines path.

11 Collisions Racks of servers 1Gbps

12 Can MPTCP self-optimize data-center traffic? With Multipath TCP we can explore many paths: Instead of using one random path, use many random paths Dont worry about collisions. Just dont send (much) traffic on colliding paths

13 Simulation Setup ~8000 hosts Long-lived flows Permutation traffic matrix Each hosts sends and receives from a single other randomly chosen host Smallest amount of traffic that can fill the network

14 Multipath TCP in the Fat Tree Topology Throughput Allocation

15 Performance depends on topology VL2 BCube

16 Overloaded Fat Tree: better fairness with Multipath TCP

17 Centralized Scheduling With RLB, its really hard to utilize FatTree. Hedera [Fares et al.,2010] uses a centralized scheduler and flow switching. Start by using RLB Measure all flow throughput periodically. Any flow using more than 10% of its interface rate is explicitly scheduled onto an unloaded link. How does centralized scheduling compare with MPTCP?

18 MPTCP vs Centralized Dynamic Scheduling Infinite Centralized Scheduling MPTCP Scheduling Interval

19 Cant we just use many TCP connections? Loss rate of MP-TCP (linked) vs multiple uncoupled TCP flows Retransmit timeouts with MPTCP (linked) vs uncoupled TCP flows

20 MPTCP Linked Increases in DCs Better fairness and less aggressive than uncoupled TCP Improves throughput in dense traffic in BCube (25%)

21 The bigger picture Topology Routing Resource Allocation FatTree, VL2, Bcube, multi-rooted tree Multipath TCP Path Selection OSPF, VLANs, etc. ?

22 Multipath TCP can utilize topologies TCP cant 1Gb/s Requirement: a subset of hosts should be able to communicate at 10Gb/s 10Gb/s

23 Multipath TCP can utilize topologies TCP cant [2] Problem ToR switch failures wipe out tens of hosts Repair time is on the order of days Solution: use two ToRs/rack, multi-home servers Single path TCP Single flows still get same max throughput Which interface do I use? With Multipath TCP Flows double their maximum throughput Path selection automatic

24 Summary Data center networking offers many paths between end-hosts. Yet: Random Load Balancing does a poor job of utilizing them Centralized scheduling is laggy and has inherently limited knowledge Multipath TCP naturally optimizes data center networks: Improves throughput Improves fairness More robust than centralized scheduling Question: what topologies does multipath TCP enable?

25 Backup Slides

26 Centralized Scheduling: Setting the Threshold Throughput 1Gbps 100Mbps Hope App Limited 17% worse than multipath TCP

27 Centralized Scheduling: Setting the Threshold Throughput 1Gbps 100Mbps Hope App Limited 21% worse than multipath TCP

28 Centralized Scheduling: Setting the Threshold Throughput 1Gbps 100Mbps 17% 21% 500Mbps 45% 51%


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